3D computational simulations of non-Newtonian shear thinning plugs propagating in capillary tubes pre-wetted with Newtonian or non-Newtonian films

Newtonian plug flow in capillary tubes is a well-researched phenomenon and is ubiquitous in many applications, such as therapeutic and biological fluid dynamics, bubbly flows, etc. On the other hand, non-Newtonian plug flow, especially its interaction with a Newtonian film, remains less understood. We use an in-house flow solver to study the film deposition of a non-Newtonian plug propagating in a capillary tube with a pre-existing non-Newtonian or Newtonian film. Using the Volume-of-Fluid framework, the flow solver employs a novel numerical scheme for capturing the interactions in three-fluid flows of two Newtonian fluids (liquid and gas) interacting with a shear thinning non-Newtonian liquid. Capturing such fluid interaction requires solving additional constitutive equations to resolve the non-Newtonian fluid dynamics. The non-Newtonian fluid is shear thinning and modeled with the Carreau-Yasuda equation. Our simulation results are also compared to experiments as well as theoretical models.